It appears that a single enzyme may act as both exopolyphosphatase (Ppx) and guanosine pentaphosphate phosphohydrolase (GppA) in a number of species. Members of the seed alignment use to define this exception-level model are encoded adjacent to a polyphosphate kinase 1 gene, and the trusted cutoff is set high enough (425) that no genome has a second hit. Therefore all members may be presumed to at least share exopolyphospatase activity, and may lack GppA activity. GppA acts in the stringent response.